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. 2022 Sep 14;96(17):e0108122.
doi: 10.1128/jvi.01081-22. Epub 2022 Aug 17.

Herpes Simplex Virus Type 1 Preferentially Enhances Neuro-Inflammation and Senescence in Brainstem of Female Mice

Affiliations

Herpes Simplex Virus Type 1 Preferentially Enhances Neuro-Inflammation and Senescence in Brainstem of Female Mice

Mahesh Kumar Sivasubramanian et al. J Virol. .

Abstract

Following acute infection, herpes simplex virus 1 (HSV-1) establishes lifelong latency in neurons. The latency associated transcript (LAT) is the only viral gene abundantly expressed during latency. Wild-type (WT) HSV-1 reactivates more efficiently than LAT mutants because LAT promotes establishment and maintenance of latency. While sensory neurons in trigeminal ganglia (TG) are important sites for latency, brainstem is also a site for latency and reactivation from latency. The principal sensory nucleus of the spinal trigeminal tract (Pr5) likely harbors latent HSV-1 because it receives afferent inputs from TG. The locus coeruleus (LC), an adjacent brainstem region, sends axonal projections to cortical structures and is indirectly linked to Pr5. Senescent cells accumulate in the nervous system during aging and accelerate neurodegenerative processes. Generally senescent cells undergo irreversible cell cycle arrest and produce inflammatory cytokines and chemokines. Based on these observations, we hypothesized HSV-1 influences senescence and inflammation in Pr5 and LC of latently infected mice. This hypothesis was tested using a mouse model of infection. Strikingly, female but not age-matched male mice latently infected with a LAT null mutant (dLAT2903) exhibited significantly higher levels of senescence markers and inflammation in LC, including cell cycle inhibitor p16, NLRP3 (NOD-, LRR- and pyrin domain-containing protein 3), IL-1α, and IL-β. Conversely, Pr5 in female but not male mice latently infected with WT HSV-1 or dLAT2903 exhibited enhanced expression of important inflammatory markers. The predilection of HSV-1 to induce senescence and inflammation in key brainstem regions of female mice infers that enhanced neurodegeneration occurs. IMPORTANCE HSV-1 (herpes simplex virus 1), an important human pathogen, establishes lifelong latency in neurons in trigeminal ganglia and the central nervous system. In contrast to productive infection, the only viral transcript abundantly expressed in latently infected neurons is the latency associated transcript (LAT). The brainstem, including principal sensory nucleus of the spinal trigeminal tract (Pr5) and locus coeruleus (LC), may expedite HSV-1 spread from trigeminal ganglia to the brain. Enhanced senescence and expression of key inflammatory markers were detected in LC of female mice latently infected with a LAT null mutant (dLAT2903) relative to age-matched male or female mice latently infected with wild-type HSV-1. Conversely, wild-type HSV-1 and dLAT2903 induced higher levels of senescence and inflammatory markers in Pr5 of latently infected female mice. In summary, enhanced inflammation and senescence in LC and Pr5 of female mice latently infected with HSV-1 are predicted to accelerate neurodegeneration.

Keywords: HSV-1; LAT; brainstem; immune senescence; inflammation; latency.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

FIG 1
FIG 1
Schematic of mouse brain, TG, and brainstem. (A) Sagittal section showing mouse brain, TG, LC, and Pr5. (B) Coronal section of mouse brain and location of LC and Pr5 in brainstem.
FIG 2
FIG 2
Comparison of senescence in LC of mice latently infected with HSV-1 versus uninfected controls. Representative images of SA-β-Gal staining showing positive cells in the LC of the brainstem in females (top panel) versus males (bottom panel). Age-matched uninfected mice were compared to mice latently infected with wild-type HSV-1 (McKRae strain) or dLAT2903 (dLAT).
FIG 3
FIG 3
Comparison of senescence in Pr5 of mice latently infected with HSV-1 versus uninfected controls. Representative images of SA-β-Gal showing positive cells in the Pr5 of the brainstem in females (top panel) versus males (bottom panel). Age-matched uninfected mice were compared to mice latently infected with wild-type HSV-1 (McKRae strain) or dLAT2903 (dLAT).
FIG 4
FIG 4
Effects of HSV-1 latent infection on senescence in Pr5 or LC. Eight-week-old mice (males and females) were infected with ~2 × 105 infectious virus particles as described in Materials and Methods. We compared gene expression between uninfected mice (U) and those infected with wild type (WT; McKRae strain) or dLAT2903 (dLAT) using primers described in Table 1. Gene expression changes in senescence markers p16, p21, or p53 were examined (n = 3-4 mice/group). * denotes significant difference (P < 0.05) between uninfected aged mice; a denotes significant difference (P < 0.05) between WT.
FIG 5
FIG 5
Effects of HSV-1 latent infection on NLRP3 expression in Pr5 or LC. (A) Schematic of key events leading to NLRP3 activation and the resulting inflammation. (B) NLRP3 RNA expression (n = 3–4 mice/group) was examined using primers described in Table 1. Expression was compared between uninfected mice (U) and those infected with WT HSV-1 (McKRae strain) or dLAT2903 (dLAT). * denotes significant difference (P < 0.05) between uninfected aged mice; a denotes significant difference (P < 0.05) between WT.
FIG 6
FIG 6
Effects of HSV-1 latent infection on inflammation in Pr5 or LC. Gene expression of IL-1α, IL-1β, TNF-α, and MCP1 (n = 3-4 mice/group) was compared in uninfected mice (U), and those infected with WT HSV-1 (McKRae strain) or dLAT2903 (dLAT) using primers described in Table 1. * denotes significant difference (P < 0.05) between uninfected aged mice; a denotes significant difference (P < 0.05) between WT.
FIG 7
FIG 7
Effects of HSV-1 latent infection on neural activity and ROS in Pr5 or LC. Gene expression of Fra-1, NRF2, and NQO1 was compared in uninfected mice (U) and those infected with WT HSV-1 (McKRae strain) or dLAT2903 (dLAT) (n = 3–4 mice/group). * denotes significant difference (P < 0.05) between uninfected aged mice; a denotes significant difference (P < 0.05) between WT.
FIG 8
FIG 8
Ocular swabs from HSV-1 infected mice. Eight-week-old C57BL/6 mice were ocularly infected with ~2 × 105 PFU either HSV-1 strain McKrae or dLAT2903 without scarification as previously described (34). Ocular swabs were obtained every other day for 10 days and then every 5 days for a total of 30 days postinfection (n = 5 mice/group). Samples were freeze-thawed three times prior to plaquing on Vero cells to measure titers of infectious virus.
FIG 9
FIG 9
Quantification of viral DNA in Pr5 and LC during acute infection and latency. Eight-week-old male (M) or female (F) C57BL/6 mice were ocularly infected with WT HSV-1 (n = 10) or dLAT2903 (n = 10). At 4 or 30 days postinfection, mice were euthanized and TG (Panel A), LC (Panel B), and Pr5 (Panel C) were harvested as described in materials and methods (n = 4 or 5 per group, per time point). DNA was prepared from tissues and qPCR performed using primers against HSV-1 gB and mouse GAPDH. Data are shown as the ratio of gB to GAPDH, max to min. *, P < 0.05 using one-way ANOVA with Tukey's multiple-comparison test.
FIG 10
FIG 10
Schematic of working model for virus–host interactions in Pr5 and LC. Following a stressful stimulus, LC in female (♀) mice exhibit higher responses because they express higher levels of corticotropin-releasing factor (CRF) receptors. Hence, they release more norepinephrine (NE), CRF, and adrenocorticotropic hormone (ACTH). This culminates in higher levels of glucocorticoids, including cortisol via the hypothalamic-pituitary-adrenal (HPA) axis. Enhanced expression of “stress-mediated” signaling pathways are predicted to increase lytic cycle viral gene expression and inflammation. Whether reactivation from latency occurs is not known. LAT expression in LC neurons, but not Pr5 neurons, is important for restricting programmed cell death (PCD), including apoptosis, inflammation, and viral gene expression. These differences in LC neurons are predicted to enhance expression of key inflammatory and SASP transcripts relative to LC or Pr5 in males (♂). Paracrine effects are predicted to enhance inflammation in Pr5 of latently infected female mice.

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